The cost of being big: local competition, importance of dispersal and experimental evolution of reversal to unicellularity

Multicellularity provides multiple benefits. Nonetheless, unicellularity is ubiquitous and there have been multiple cases of evolutionary reversal to a unicellular organization. In this paper, we explore some of the costs of multicellularity as well as the possibility and dynamics of evolutionary reversals to unicellularity. We hypothesize that recently evolved multicellular organisms would face a high cost of increased competition for local resources in spatially structured environments because of larger size and increased cell densities. To test this hypothesis we conducted competition assays, computer simulations, and selection experiments using isolates of Saccharomyces cerevisiae that recently evolved multicellularity. In well-mixed environments, multicellular isolates had lower growth rates relative to their unicellular ancestor due to limitations of space and resource acquisition. In structured environments with localized resources, cells in both multicellular and unicellular iso...多细胞性（Multicellularity）具备多重优势。尽管如此，单细胞性（unicellularity）仍广泛分布，且进化逆转至单细胞组织结构的案例已多次出现。本研究旨在探讨多细胞性的部分代价，以及进化逆转至单细胞状态的可能性与动力学机制。我们提出假说：新近演化出多细胞性的生物，由于体型更大、细胞密度更高，在空间结构化环境中会面临局部资源竞争加剧的高昂代价。为验证该假说，我们以新近演化出多细胞性的酿酒酵母（Saccharomyces cerevisiae）分离株为实验材料，开展了竞争实验、计算机模拟与选择实验。在充分混合的环境中，多细胞分离株相较于其单细胞祖先，因空间与资源获取受限，生长速率更低。在带有局部资源的结构化环境中，多细胞与单细胞分离株的细胞……